1. Field of the Invention
The present invention relates to a digital controller that receives an analog signal as an input and converts the analog signal into a digital signal to be processed, and more particularly, to an input process that takes into consideration a disconnection or a short circuit of an input signal line to which an analog input signal is input.
2. Description of the Related Art
As the device of the above type, for example, JP 08-338296 A discloses a vehicle controller that is capable of precisely discriminating the disconnection of a ground conductor from the disconnection of a signal line or a normal state. In the vehicle controller, an oil temperature sensor, a water temperature sensor, and an engine speed sensor share the ground terminal, and signal lines are connected to the respective input circuits. The microcomputer circuit detects a detection signal of the oil temperature sensor, and intermittently and repetitively discriminates whether the detection signal falls within a predetermined failure detection range, or not. Then, when the number of times the detection signal is determined as the failure detection range reaches a given limit value, an engine and an automatic transmission are caused to execute a fail safe control. Since the ground terminal is shared by the respective sensors, the number of connector pins and the number of wirings are reduced, and there is no need to provide a specific circuit for detecting the disconnection of the ground conductor.
In the above device, when a disconnection or a short circuit occurs in the input signal line from the sensor, an abnormal sensor value, that is, an abnormal input value is input until the disconnection or the short circuit is detected, which causes the possibility that a malfunction occurs in the controller or a control system having the controller, or an abnormal sensor value is displayed on a display unit.